Terms Starting with H
Harmonics-When valve springs are opened and closed rapidly, they may vibrate. Periods of vibration are called harmonics.
Header-Welded steel pipe used as an exhaust manifold.
Heat dam-The narrow groove cut into the top of the piston. It restricts the flow of heat down into the piston.
Heater core-A small radiator-like heat exchanger. Hot coolant from the engine flows through the heater core. Airflow from a fan passes through the fins on the heater core, picking up heat to warm the passenger compartment.
Heat exchanger-A device used to transfer heat from one medium to another. The radiator is a liquid-to-air heat exchanger.
Heat stove-An enclosed area made of thin sheet metal around the exhaust manifold. It preheats air passing over the exhaust manifold before the air enters the air cleaner.
Heat transfer-The process of moving heat from a warmer object to a colder object.
Heat treated-A process in which a metal is heated to a high temperature, then quenched in a cool bath of water, oil, or brine (salt water). This process hardens the metal.
HEI-High-energy ignition system: A type of ignition system used on vehicles in which the coil and distributor are physically combined into one unit.
Hemispherical combustion chamber-A type of combustion chamber that is shaped like a half circle. This combustion chamber has the valves on either side with the spark plug in the center.
High test-Gasoline that has an octane number of 90 to 95.
Horsepower-A measure of work being done per time unit. One hp equals the work done when 33,000 pounds have been lifted 1 foot in 1 minute.
Hydraulic system-A brake system in which brakes are operated and controlled by hydraulic fluid under pressure.
Hydrocarbons-A term used to describe the chemical combinations of hydrogen and carbon. Also, a type of automotive pollution produced by incomplete combustion. Hydrocarbons are considered partly burned hydrogen and carbon molecules resulting from incomplete combustion.
Hydrometer-An instrument used to measure the specific gravity of a battery acid.
Hypoid gear oil-A thick oil used in differentials.
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